Display device and electronic apparatus

ABSTRACT

According to an aspect, a display device includes a plurality of pixels each including a plurality of sub-pixels. Each of the sub-pixels is arranged around center of the corresponding pixel and divided into a plurality of display regions to perform N-bit area coverage modulation by a combination of the display regions. The display regions are arranged in such a manner that: a display region corresponding to a least significant bit of the area coverage modulation is arranged closest to the center of the corresponding pixel; and a display region corresponding to a higher significant bit of the area coverage modulation is arranged around the center of the pixel and further from the center of the corresponding pixel (N is a natural number of 2 or more).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Japanese Application No.2013-063107, filed on Mar. 25, 2013, the contents of which areincorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a display device and an electronicapparatus including the same.

2. Description of the Related Art

In recent years, demand has been increasing for a display device for amobile apparatus such as a cellular telephone or an electronic paper, oran on-vehicle display device. In some display devices, one pixelincludes a plurality of sub-pixels, and the sub-pixels output light indifferent colors and are switched on and off to display various colorswith one pixel. Examples of such a display device include, but are notlimited to, a display device in which one pixel is divided into aplurality of display regions to express gradation by a combination ofthe display regions, which is area coverage modulation (for example,refer to Japanese Patent Application Laid-open Publication No.05-181131).

The area coverage modulation requires division of pixels (sub-pixels forcolor display) into a plurality of pieces. Accordingly, an electrodeincluded in the pixel is also divided and the number of couplingportions to a signal line increases according to the number of division.As a result, the display regions may reduce in a transmissive displaydevice that performs display utilizing transmitted light of backlightfrom the back surface of a screen. In a reflective display device thatperforms display utilizing reflected light of external light and atransflective liquid crystal display device including a transmissivedisplay region (transmissive display part) and a reflective displayregion (reflective display part) in one pixel, an area of the reflectivedisplay part that can be used for reflective display may reduce. Whenthe area coverage modulation is performed, the gradation may not besufficiently expressed depending on the arrangement of the dividedregions.

For the foregoing reasons, there is a need for reducing effects ondisplay quality caused by dividing the sub-pixel when the area coveragemodulation is performed.

SUMMARY

According to an aspect, a display device includes a plurality of pixelseach including a plurality of sub-pixels. Each of the sub-pixels isarranged around center of the corresponding pixel and divided into aplurality of display regions to perform N-bit area coverage modulationby a combination of the display regions. The display regions arearranged in such a manner that: a display region corresponding to aleast significant bit of the area coverage modulation is arrangedclosest to the center of the corresponding pixel; and a display regioncorresponding to a higher significant bit of the area coveragemodulation is arranged around the center of the pixel and further fromthe center of the corresponding pixel (N is a natural number of 2 ormore).

According to an aspect, an electronic apparatus includes the displaydevice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cutout perspective view illustrating a schematicconfiguration of a transflective liquid crystal display device to whichthe present disclosure is applied;

FIG. 2 is a diagram illustrating an example of a pixel circuit;

FIG. 3 is a plan view illustrating the electrode structure of a pixelpart according to an embodiment;

FIG. 4 is a cross-sectional view illustrating a transflective liquidcrystal display device to which the present disclosure is applied;

FIG. 5 is a cross-sectional view illustrating an example of a lightscattering film;

FIG. 6 is a plan view illustrating the example of the light scatteringfilm;

FIG. 7 is a plan view illustrating a modification of the lightscattering film;

FIG. 8 is a block diagram illustrating an example of a circuitconfiguration of a pixel employing the MIP technology;

FIG. 9 is a timing chart illustrating an operation of the pixelemploying the MIP technology;

FIG. 10 is a diagram illustrating a pixel of the transflective liquidcrystal display device according to the present embodiment;

FIG. 11 is a diagram illustrating gradation expression with the pixel ofthe transflective liquid crystal display device according to the presentembodiment;

FIG. 12 is an enlarged view of a coupling part of a first divided pixeland a second divided pixel;

FIG. 13 is a diagram illustrating one sub-pixel;

FIG. 14 is a diagram illustrating gradation expression with a pixelaccording to a first comparative example;

FIG. 15 is a diagram illustrating gradation expression with a pixelaccording to a second comparative example;

FIG. 16 is a diagram illustrating a pixel according to a thirdcomparative example;

FIG. 17 is a diagram illustrating gradation expression with a pixelaccording to the third comparative example;

FIG. 18 is a diagram illustrating a pixel according to a firstmodification of the present embodiment;

FIG. 19 is a diagram illustrating a pixel according to a secondmodification of the present embodiment;

FIG. 20 is a diagram illustrating a television apparatus to which thetransflective liquid crystal display device is applied;

FIG. 21 is a diagram illustrating a digital camera to which thetransflective liquid crystal display device is applied;

FIG. 22 is a diagram illustrating the digital camera to which thetransflective liquid crystal display device is applied;

FIG. 23 is a diagram illustrating the external appearance of a videocamera to which the transflective liquid crystal display device isapplied;

FIG. 24 is a diagram illustrating a laptop personal computer to whichthe transflective liquid crystal display device is applied;

FIG. 25 is a front view of a mobile phone in an open state to which thepresent disclosure is applied;

FIG. 26 is a right side view of the mobile phone in the open state towhich the present disclosure is applied;

FIG. 27 is a top view of the mobile phone in a folded state to which thepresent disclosure is applied;

FIG. 28 is a left side view of the mobile phone in the folded state towhich the present disclosure is applied;

FIG. 29 is a right side view of the mobile phone in the folded state towhich the present disclosure is applied;

FIG. 30 is a rear view of the mobile phone in the folded state to whichthe present disclosure is applied;

FIG. 31 is a front view of the mobile phone in the folded state to whichthe present disclosure is applied; and

FIG. 32 is a diagram illustrating an information portable terminal towhich the present disclosure is applied.

DETAILED DESCRIPTION

The following describes modes for implementing the technique of thepresent disclosure (hereinafter, referred to as “embodiments”) in detailwith reference to the accompanying drawings in the following procedures.

1. Liquid crystal display device to which the present disclosure isapplied

-   -   1-1. Transflective liquid crystal display device for color        display    -   1-2. Example of pixel circuit    -   1-3. Electrode structure of pixel part    -   1-4. Scattering layer and spacer    -   1-5. MIP technology    -   1-6. Area coverage modulation    -   1-7. First modification    -   1-8. Second modification

2. Electronic apparatus

3. Configuration of present disclosure

1. Liquid Crystal Display Device to which the Present Disclosure isApplied

The technique of the present disclosure can be applied to a flat panel(planar) display device. Examples of the flat panel display deviceinclude, but are not limited to, a display device using a liquid crystaldisplay (LCD) panel, and a display device using an electro luminescence(EL) display panel.

The flat panel display devices can be classified into a transmissivetype, a reflective type, and a transflective type according to a displaytype. The technique of the present disclosure can be applied to atransmissive liquid crystal display device, a reflective liquid crystaldisplay device, and a transflective liquid crystal display device havingcharacteristics of both the transmissive display device and thereflective display device. The liquid crystal display device accordingto the present disclosure is preferably used as a display unit of anelectronic apparatus, especially as a portable electronic apparatusfrequently used outdoors such as a portable information apparatus (adigital camera, for example) or a portable communication apparatus (amobile phone, for example).

The liquid crystal display device to which the present disclosure isapplied may be a display device for monochromatic display or a displaydevice for color display. In the display device for color display, onepixel (unit pixel) as a unit forming a color image includes a pluralityof sub-pixels. More specifically, in the display device for colordisplay, for example, the unit pixel includes three sub-pixels of asub-pixel representing red (R), a sub-pixel representing green (G), anda sub-pixel representing blue (B).

The pixel is not limited to a pixel including sub-pixels of the threeprimary colors (RGB). For example, the unit pixel may be made by addingsub-pixels of one color or a plurality of colors to the sub-pixels ofthe three primary colors (RGB). More specifically, for example, the unitpixel may be made by adding a sub-pixel representing white (W) forimproving luminance, or the unit pixel may be made by adding at leastone sub-pixel representing a complementary color to expand the range ofcolor reproduction.

1-1. Transflective Liquid Crystal Display Device for Color Display

The following describes a transflective liquid crystal display devicefor color display as an example of the liquid crystal display device towhich the present disclosure is applied with reference to the drawings.The present disclosure is not limited to color display. Not limited tothe transflective liquid crystal display device, the present disclosurecan be applied to a transmissive liquid crystal display device and areflective liquid crystal display device.

FIG. 1 is a partially cutout perspective view illustrating a schematicconfiguration of a transflective liquid crystal display device to whichthe present disclosure is applied. As illustrated in FIG. 1, thistransflective liquid crystal display device 1 as the liquid crystaldisplay device to which the present disclosure is applied includes afirst panel unit 10, a second panel unit 20, a liquid crystal layer 30,and a backlight unit 40, as main components. In the transflective liquidcrystal display device 1, the surface side of the second panel unit 20is a display surface side. The first panel unit 10 and the second panelunit 20 are arranged opposite to each other with a predetermined gaptherebetween. The liquid crystal layer 30 is formed by filling liquidcrystal material in the gap between the first panel unit 10 and thesecond panel unit 20.

The first panel unit 10 includes a polarizing plate 11, a ½ wavelengthplate 12, a ¼ wavelength plate 13, a first substrate 14 formed oftransparent glass or the like, and a planarization film 15 in this orderon the side remote from the liquid crystal layer 30, that is, thebacklight unit 40 side.

In the first panel unit 10, a plurality of signal lines and a pluralityof scanning lines (both are not illustrated) are formed to intersectwith each other on the first substrate 14. At parts where the signallines and the scanning lines intersect with each other, the sub-pixels(hereinafter, simply referred to as “pixels” in some cases) 50 aretwo-dimensionally arranged in a matrix.

Circuit elements including a switch element such as a thin filmtransistor (TFT) and a capacitive element are also formed on the firstsubstrate 14 for each pixel 50. The planarization film 15 is formed onthe surface of the circuit element, the signal lines, and the scanninglines to flatten the surface of the first panel unit 10. Then areflective electrode to be described later is formed on theplanarization film 15 for each pixel 50. The first substrate 14 may bereferred to as a TFT substrate because the circuit elements thus formedinclude the TFT.

The signal lines are wiring for transmitting a signal (displaysignal/video signal) that drives the pixel 50, and have a wiringstructure extending along the arrangement direction of pixels of a pixelcolumn, which is the column direction (Y-direction in FIG. 1), for eachpixel column of the matrix of the pixels 50. The scanning lines arewiring for transmitting a signal (scanning signal) that selects thepixels 50 for each raw, and have a wiring structure extending along thearrangement direction of pixels of a pixel row, which is the rowdirection (X-direction in FIG. 1), for each pixel row of the matrix ofthe pixels 50. The X-direction and the Y-direction are orthogonal toeach other.

The second panel unit 20 includes a transparent electrode 21 formed ofindium tin oxide (ITO) or the like, a color filter 22, a secondsubstrate 23 formed of transparent glass or the like, a scattering layer27, a ¼ wavelength plate 24, a ½ wavelength plate 25, and a polarizingplate 26 arranged in this order from the liquid crystal layer 30 side.

In the second panel unit 20, the color filter 22 has a configuration inwhich respective stripe-shaped filters of R (red), G (green), and B(blue) extending in the column direction (Y-direction) for example arerepeatedly arranged at a pitch same as the pitch of the pixel 50 in therow direction (X-direction). The second substrate 23 may be referred toas a CF substrate because it includes the color filter (CF) 22.

A transflective liquid crystal display panel includes the first panelunit 10, the second panel unit 20 opposed to the first panel unit 10,and the liquid crystal layer 30 arranged between the first panel unit 10and the second panel unit 20. The upper surface (front surface) of thesecond panel unit 20 is a display surface.

The backlight unit 40 is an illumination unit that illuminates theliquid crystal display panel from the back surface side thereof, thatis, the side opposed to the liquid crystal layer 30 of the first panelunit 10. The backlight consists of well-known members such as a lightemitting diode (LED) or a fluorescent tube as a light source, and awell-known member such as a prism sheet, a diffusion sheet, and alight-guiding plate. However, the members for the back light are notlimited to them.

In the transflective liquid crystal display device 1 having the abovestructure, each of the pixels 50 includes a reflective display region(reflective display part) and a transmissive display region(transmissive display part). As described above, the reflective displayregion includes the reflective electrode formed for each pixel 50 on thesurface of the planarization film 15. The reflective electrode reflectsexternal light incident from the outside through the second panel unit20 to be used for display. The transmissive display region transmitslight from the backlight unit 40 and performs display using thetransmitted light. Details of the transmissive display region providedfor each pixel 50 will be described later.

1-2. Example of Pixel Circuit

An example of the pixel circuit of the pixel 50 will be described withreference to FIG. 2. The direction indicated by “X” in FIG. 2(X-direction) indicates the row direction of the transflective liquidcrystal display device 1 illustrated in FIG. 1, and the directionindicated by “Y” (Y-direction) in FIG. 2 indicates the column directionin FIG. 1.

FIG. 2 is a diagram illustrating an example of a pixel circuit. Asillustrated in FIG. 2, a plurality of signal lines 61 (61 ₁, 61 ₂, 61 ₃,. . . ) are arranged orthogonally to a plurality of scanning lines 62(62 ₁, 62 ₂, 62 ₃, . . . ), and the pixels 50 are arranged atintersection parts thereof. The scanning lines 62 (62 ₁, 62 ₂, 62 ₃, . .. ) extend in the row direction (X-direction), and the signal lines 61(61 ₁, 61 ₂, 61 ₃, . . . ) extend in the column direction (Y-direction).As described above, the signal lines 61 and the scanning lines 62 areformed on a surface of the first substrate (TFT substrate) 14 of thefirst panel unit 10. One end of each of the signal lines 61 (61 ₁, 61 ₂,61 ₃, . . . ) is coupled to a corresponding output of a signal outputcircuit 70, and one end of each of the scanning lines 62 (62 ₁, 62 ₂, 62₃, . . . ) is coupled to a corresponding output of a scanning circuit80.

For example, the pixel 50 includes a pixel transistor 51 employing athin film transistor (TFT), a liquid crystal capacitor 52, and a holdingcapacitor 53. The gate electrode of the pixel transistor 51 is coupledto the scanning line 62 (62 ₁, 62 ₂, 62 ₃, . . . ), and the sourceelectrode of the pixel transistor 51 is coupled to the signal line 61(61 ₁, 61 ₂, 61 ₃, . . . ).

The liquid crystal capacitor 52 means a capacitive component of liquidcrystal material generated between a pixel electrode and a counterelectrode formed opposite thereto (corresponding to the transparentelectrode 21 in FIG. 1), and the pixel electrode is coupled to the drainelectrode of the pixel transistor 51. In color display, the pixelelectrode corresponds to the reflective electrode formed for eachsub-pixel, whereas in monochromatic display, the pixel electrodecorresponds to the reflective electrode formed for each pixel. Thedirect current voltage at a common potential V_(COM) is applied to thecounter electrode of the liquid crystal capacitor 52 in each of thepixels. One electrode of the holding capacitor 53 is coupled to thepixel electrode of the liquid crystal capacitor 52, and the otherelectrode of the holding capacitor 53 is coupled to the counterelectrode of the liquid crystal capacitor 52.

As is clear from the pixel circuit described above, the signal lines 61(61 ₁, 61 ₂, 61 ₃, . . . ) are wiring that transmits a signal fordriving the pixel 50, which is a video signal output from the signaloutput circuit 70, to the pixels 50 in each pixel column. The scanninglines 62 (62 ₁, 62 ₂, 62 ₃, . . . ) are wiring that transmits a signalfor selecting the pixels 50 for each row, which is the scanning signaloutput from the scanning circuit 80 for each pixel row.

1-3. Electrode Structure of Pixel Part

FIG. 3 is a plan view illustrating the electrode structure of a pixelpart according to an embodiment. The transflective liquid crystaldisplay device 1 performs transmissive display using a space between thepixels 50 of a reflective electrode 63 while maintaining reflectiondisplay performance equivalent to that of the reflective display device.Specifically, as illustrated in FIG. 3, the wiring of signal lines 61,scanning lines 62, and the like is formed so as not to block the spacebetween the pixels 50 of the reflective electrode 63 in the pixel partin which the pixels 50 are arranged in a matrix. Accordingly, thetransmissive display can be performed using the space as thetransmissive display region.

In FIG. 3, the reflective electrode 63 is illustrated by hatching. Thespace between the pixels 50 of the reflective electrode 63 includes aspace 65 _(A) extending along the arrangement direction of the pixels ofthe pixel column, which is the column direction (Y-direction illustratedin FIG. 3), and a space 65 _(B) extending along the arrangementdirection of the pixels of the pixel row, which is the row direction(X-direction illustrated in FIG. 3). The present example illustrates thesignal line 61 and the scanning line 62 as the wiring formed in thepixel part. However, the wiring formed in the pixel part is not limitedthereto. That is, all driving lines (control lines) required for driving(controlling) the pixel 50 are the wiring according to the example.

The phrase “not to block the space” does not exclude a case in whichthere is a region where the wiring overlaps with the spaces 65 _(A) and65 _(B) between the pixels 50 of the reflective electrode 63.Specifically, the concept of “not to block the space” includes a statein which the signal line 61 wired in the column direction overlaps withthe space 65 _(B) extending in the row direction, and a state in whichthe scanning line 62 wired in the row direction overlaps with the space65 _(A) extending in the column direction.

The concept of “not to block the space” also includes a state in whichthe signal line 61 partly or partially overlaps with the space 65 _(A)extending in the column direction, and a state in which the scanningline 62 partly or partially overlaps with the space 65 _(B) extending inthe row direction. In both cases, a region where the signal line 61 andthe scanning line 62 do not overlap with the spaces 65 _(A) and 65 _(B),respectively, is used as the transmissive display region.

Not to block the spaces 65 _(A) and 65 _(B) between the pixels 50 of thereflective electrode 63, the wiring is preferably formed away from thespaces 65 _(A) and 65 _(B) between the pixels 50 of the reflectiveelectrode 63. The phrase “away from the spaces” means a state in whichwiring does not entirely cover the spaces 65 _(A) and 65 _(B) betweenthe pixels 50 of the reflective electrode 63 (that is, there is noregion where the wiring entirely overlaps with the spaces 65 _(A) and 65_(B)).

Specifically, as illustrated in FIG. 3, the signal line 61 is preferablywired away from the space 65 _(A) extending in the column direction,that is, having no region (portion) entirely overlapping with the space65 _(A). The scanning line 62 is preferably wired away from the space 65_(B) extending in the row direction, that is, having no region entirelyoverlapping with the space 65 _(B). The entire regions of the spaces 65_(A) and 65 _(B) can be used as the transmissive display region becausethere is no region overlapping with the signal line 61 and the scanningline 62 in the spaces 65 _(A) and 65 _(B) between the pixels 50 of thereflective electrode 63, so that the transflective liquid crystaldisplay device 1 can obtain higher transmissive display performance.

As described above, the transflective liquid crystal display device 1performs transmissive display using the space between the pixels 50 ofthe reflective electrode 63, that is, the space is used as thetransmissive display region. Accordingly, it is not necessary toseparately secure the transmissive display region in the pixel 50. Inthis way, as is clear from FIG. 3, the dimensions of individual piecesof the reflective electrode 63 are equivalent to the dimensions of thoseof the reflective liquid crystal display device when the pixels 50 havethe same size in the transflective liquid crystal display device 1. As aresult, the transflective liquid crystal display device 1 can achievetransmissive display while maintaining the reflection displayperformance equivalent to that of the reflective display device.

1-4. Scattering Layer and Spacer

FIG. 4 is a cross-sectional view illustrating the transflective liquidcrystal display device to which the present disclosure is applied. Asillustrated in FIG. 4, the scattering layer 27, the ¼ wavelength plate24 as a wave plate, the ½ wavelength plate 25 as a wave plate, and thepolarizing plate 26 are arranged in this order on the opposite side ofthe second substrate 23 to the color filter 22. The scattering layer 27is provided in the traveling direction of light reflected by thereflective electrode 63. The scattering layer 27 is an anisotropic orisotropic layer that scatters light reflected by the reflectiveelectrode 63 and backlight transmitted through the space 65 _(A) betweenthe pixels. The scattering layer 27 includes two light scattering films271. The two light scattering films 271 are laminated in a directionaway from the second substrate 23. The light scattering film 271 mayhave one layer or three or more layers. It is preferable that the lightscattering film 271 has a plurality of layers because the diffusionrange of light can be expanded and iridescence can be more securelyreduced.

As illustrated in FIG. 4, a spacer SP is provided between thetransparent electrode 21 and the reflective electrode 63. The spacer SPkeeps a constant interval between the transparent electrode 21 and thereflective electrode 63, and forms a space in which the liquid crystallayer 30 is provided therebetween. The liquid crystal layer 30 is formedof liquid crystal molecules provided between the transparent electrode21 and the reflective electrode 63.

FIG. 5 is a cross-sectional view illustrating an example of the lightscattering film, FIG. 6 is a plan view illustrating the example of thelight scattering film, and FIG. 7 is a plan view illustrating amodification of the light scattering film. For example, a light controlfilm (LCF) may be used as the light scattering film 271. The lightscattering film 271 is a forward scattering layer that largely scatterslight forward and scarcely scatters light backward. The light scatteringfilm 271 is an anisotropic scattering film that scatters light incidentfrom a specific direction. When light is incident from a specificdirection on the polarizing plate 26 side with respect to the secondsubstrate 23, the light scattering film 271 transmits the incident lightalmost without scattering, and largely scatters the returned lightreflected by the reflective electrode 63.

For example, as illustrated in FIG. 5, the light scattering film 271transmits external light L1 incident from a light emitting body LS (forexample, illumination or the sun) in a predetermined direction withrespect to the second substrate 23, and scatters light L2 thustransmitted and reflected by the reflective electrode 63 (reflectedlight) within a predetermined range around a scattering center axis AXL.The external light L1 is parallel light incident on the polarizing plate26 of the second substrate 23. The external light L1 may be unpolarizedlight or polarized light. For example, as illustrated in FIG. 6, thelight scattering film 271 includes two types of regions (a first region27B and a second region 27S) having different refractive indexes. Thelight scattering film 271 may have a louver structure in which aplurality of plate-shaped second regions 27S are arranged atpredetermined intervals in the first region 27B as illustrated in FIG.6, or may have a pillar-shaped structure in which pillar-shaped secondregions 27Sa are arranged in the first region 27B like a lightscattering film 271 a illustrated in FIG. 7.

For example, in the light scattering film 271, the first region 27B andthe second region 27S extend in the thickness direction and incline in apredetermined direction. For example, the light scattering film 271 isformed by obliquely irradiating a resin sheet with ultraviolet rays, theresin sheet being a composite of two or more types of photopolymerizablemonomer or oligomer of which refractive indexes are different from eachother. The light scattering film 271 may have a different structure fromthe above, and may be manufactured in a method different from the above.In a case in which the scattering layer 27 includes the light scatteringfilms 271, the light scattering films 271 may have the same structure ormay have different structures from each other.

The scattering center axis AXL of the light scattering film 271 ispreferably oriented, for example, toward the direction of a main visualangle α (main visual angle direction) of the transflective liquidcrystal display device 1 illustrated in FIG. 1. The scattering centeraxis AXL may be oriented toward a direction different from the mainvisual angle direction. In both cases, the orientation of the scatteringcenter axis AXL may be set so that luminance in the main visual angledirection is the brightest, that is, the reflectivity in the directionis the highest due to the light scattering film 271, when the lightscattering film 271 is used. The main visual angle α corresponds to adirection from which a user of the transflective liquid crystal displaydevice 1 views a video display surface when using the transflectiveliquid crystal display device 1. For example, when the video displaysurface has a rectangular shape, the main visual angle directioncorresponds to a direction orthogonal to a side closest to the useramong the sides of the video display surface.

When the backlight or the like is transmitted through the space 65 _(A)between the pixels, a variation in the transmission of the backlight orthe like may increase due to the patterning accuracy of the reflectiveelectrode 63 or misalignment with respect to the second substrate 23.Especially, when silver is used for the reflective electrode 63 througha wet process, the variation described above may significantly increase.When the scattering layer 27 including the light scattering film 271 isused, the transmitted light is scattered, so that it is advantageousthat the variation described above is leveled.

1-5. MIP Technology

To perform transmissive display using a space between the pixels 50 ofthe reflective electrode 63, a frame inversion driving method ispreferably used rather than a line inversion driving method or a dotinversion driving method. Employment of the line inversion drivingmethod or the dot inversion driving method is not excluded. In the frameinversion driving method, shading may occur because a signal voltage ofthe same polarity is written to the signal line over one frame period.In the frame inversion driving method, the transflective liquid crystaldisplay device 1 employs a pixel having a memory function as the pixel50. This is called the MIP (Memory In Pixel) technology, in which eachpixel has a memory capable of storing therein data. In the MIPtechnology, shading can be reduced because a constant voltage is alwaysapplied to the pixel 50.

In the MIP technology, the pixel includes a memory that stores thereindata, achieving display in an analog display mode and display in amemory display mode. The analog display mode is a display mode toanalogically display the gradation of the pixel. The memory display modeis a display mode to digitally display the gradation of the pixel basedon binary information (logical “1”/logical “0”) stored in the memory inthe pixel.

The information held in the memory is used in the memory display mode,eliminating the need to perform a writing operation of a signalpotential reflecting the gradation in a frame cycle. Accordingly, powerconsumption in the memory display mode is lower than that in the analogdisplay mode in which the writing operation of the signal potentialreflecting the gradation is performed in a frame cycle. In other words,the power consumption in the transflective liquid crystal display device1 can be reduced.

FIG. 8 is a block diagram illustrating an example of a circuitconfiguration of the pixel employing the MIP technology, where the samecomponents as those in FIG. 2 are denoted by the same referencenumerals. FIG. 9 is a timing chart illustrating an operation of thepixel employing the MIP technology.

As illustrated in FIG. 8, the pixel 50 includes a drive circuit unit 58including three switch elements 54, 55, and 56 and a latch unit 57, inaddition to the liquid crystal capacitor (liquid crystal cell) 52. Thedrive circuit unit 58 includes a static random access memory (SRAM)function. The pixel 50 including the drive circuit unit 58 has a pixelconfiguration with the SRAM function. The liquid crystal capacitor(liquid crystal cell) 52 means a liquid crystal capacitor generatedbetween the pixel electrode (for example, the reflective electrode 63 inFIG. 3) and the counter electrode opposed thereto.

One end of the switch element 54 is coupled to the signal line 61(corresponding to the signal lines 61 ₁ to 61 ₃ in FIG. 2). The switchelement 54 is switched to an “ON” (closed) state when a scanning signalφV is given from the scanning circuit 80 in FIG. 2, and captures dataSIG supplied from the signal output circuit 70 in FIG. 2 via the signalline 61. The latch unit 57 includes inverters 571 and 572 that arecoupled in parallel in mutually opposite directions. The latch unit 57holds (latches) an electric potential corresponding to the data SIGcaptured by the switch element 54.

A control pulse XFRP having the opposite phase to the common potentialV_(COM) and a control pulse FRP having the same phase as the commonpotential V_(COM) are given to one terminal of each of the switchelements 55 and 56. The other terminal of each of the switch elements 55and 56 is coupled in common, and this common connection node N_(out) isan output node N_(out) of the pixel circuit. Any one of the switchelements 55 and 56 is switched to the “ON” state depending on thepolarity of the holding potential of the latch unit 57. Accordingly, thecontrol pulse FRP or the control pulse XFRP is applied to the pixelelectrode (for example, the reflective electrode 63 in FIG. 3) of theliquid crystal capacitor 52 in which the common potential V_(COM) isapplied to the counter electrode (the transparent electrode 21 in FIG.1).

As is clear from FIG. 9, when the holding potential of the latch unit 57has a negative polarity in this example, the pixel potential of theliquid crystal capacitor 52 has the same phase as the common potentialV_(COM), so that black is displayed. When the holding potential of thelatch unit 57 has a positive polarity, the pixel potential of the liquidcrystal capacitor 52 has the opposite phase to the common potentialV_(COM), so that white is displayed.

As is clear from the above description, in the pixel 50 using the MIPtechnology, when any one of the switch elements 55 and 56 is switched tothe “ON” state depending on the polarity of the holding potential of thelatch unit 57, the control pulse FRP or the control pulse XFRP isapplied to the pixel electrode (for example, the reflective electrode 63in FIG. 3) of the liquid crystal capacitor 52. As a result, a constantvoltage is always applied to the pixel 50, reducing the shading.

The present example describes using the SRAM as a memory incorporated inthe pixel 50. However, the SRAM is an example, and other memory such asa dynamic random access memory (DRAM) may be used.

1-6. Area Coverage Modulation

The area coverage modulation method is employed for reducing unevennessin the display quality due to variation in TFT characteristics, forexample. In the MIP technology, only two gradations are expressed with 1bit for each pixel 50. When the transflective liquid crystal displaydevice 1 employs the MIP technology, the area coverage modulation methodmay be preferably used. The area coverage modulation method is agradation expression method of expressing four gradations with 2 bits byweighting a pixel area (the area of the pixel electrode) by 2:1, forexample.

Specifically, the area coverage modulation method is used for dividingthe reflective electrode 63 (refer to FIG. 3) as a reflective displayregion of the pixel (sub-pixel) 50 into a plurality of electrodes thatare areally weighted. The pixel potential selected by the holdingpotential of the latch unit 57 is applied to the divided pixel electrodethat is areally weighted to perform gradation display by a combinationof weighted areas. Hereinafter, display regions obtained by areallyweighting and dividing the sub-pixel 50 are referred to as “dividedpixels”. The reflective electrode 63 illustrated in FIG. 3 correspondsto the sub-pixel 50 illustrated in FIG. 1. Electrodes obtained byareally weighting and dividing the reflective electrode 63 are referredto as “divided pixel electrodes.”

The area coverage modulation method will be specifically describedbelow. The area coverage modulation method is a gradation expressionmethod in which 2×N gradations are expressed with N electrodes weightedin such an area ratio that their areas are proportionally 2⁰, 2¹, 2², .. . , 2^(N-1) (where one electrode corresponds to a bit for displayingthe gradation). When a plurality of electrodes correspond to the bit fordisplaying the gradation, in the area coverage modulation method, theelectrodes corresponding to the bit are weighted in such an area ratiothat their areas are proportionally 2⁰, 2¹, 2², . . . , 2^(N-1), therebydisplaying 2^(N) gradation with N bits (N is a natural number of 2 ormore).

FIG. 10 is a diagram illustrating a pixel of the transflective liquidcrystal display device according to the present embodiment. A pixel PXincludes sub-pixels 50B, 50R, 50G, and 50W. The sub-pixel 50B representsblue, the sub-pixel 50R represents red, the sub-pixel 50G representsgreen, and the sub-pixel 50W represents white.

The sub-pixel 50B includes a first divided pixel 50B1 and a seconddivided pixel 50B2. The sub-pixel 50R includes a first divided pixel50R1 and a second divided pixel 50R2. The sub-pixel 50G includes a firstdivided pixel 50G1 and a second divided pixel 50G2. The sub-pixel 50Wincludes a first divided pixel 50W1 and a second divided pixel 50W2. Inthe present embodiment, the area ratio between the first divided pixel50B1 and the second divided pixel 50B2 is 1:2, the area ratio betweenthe first divided pixel 50R1 and the second divided pixel 50R2 is 1:2,the area ratio between the first divided pixel 50G1 and the seconddivided pixel 50G2 is 1:2, and the area ratio between the first dividedpixel 50W1 and the second divided pixel 50W2 is 1:2. These area ratiosare not limited to 1:2, and may be changed as appropriate according tothe specifications of the transflective liquid crystal display device 1or the characteristics of the color filter 22, and the like.

The sub-pixels 50B, 50R, 50G, and 50W included in the pixel PX arearranged around the center PXC of the pixel PX. The sub-pixels 50B, 50R,50G, and 50W are divided into a plurality of display regions, that is,the first divided pixels 50B1, 50R1, 50G1, and 50W1 and the seconddivided pixels 50B2, 50R2, 50G2, and 50W2, respectively. The respectivesub-pixels 50B, 50R, 50G, and 50W can achieve N-bit area coveragemodulation by a combination of the first divided pixels 50B1, 50R1,50G1, and 50W1 and the second divided pixels 50B2, 50R2, 50G2, and 50W2.

The first divided pixels 50B1, 50R1, 50G1, and 50W1 are display regionscorresponding to the least significant bit in the N-bit (in thisembodiment, N=2 bits) area coverage modulation. The second dividedpixels 50B2, 50R2, 50G2, and 50W2 are display regions corresponding tothe most significant bit in the N-bit (in this embodiment, N=2 bits)area coverage modulation. The first divided pixels 50B1, 50R1, 50G1, and50W1 include divided electrodes 501B1, 501R1, 501G1, and 501W1 asreflective electrodes, respectively. The first divided pixels 50B1,50R1, 50G1, and 50W1 include divided electrodes 501B2, 501R2, 501G2, and501W2 as reflective electrodes, respectively.

The display regions corresponding to the least significant bit, that is,the first divided pixels 50B1, 50R1, 50G1, and 50W1 are arranged closestto the center PXC of the pixel PX. The display regions corresponding toa higher significant bit of the area coverage modulation, that is, thesecond divided pixels 50B2, 50R2, 50G2, and 50W2 are arranged away fromthe center PXC of the pixel PX.

The center PXC of the pixel PX is the centroid of the pixel PX in a planview in which the pixel PX is viewed from the direction orthogonal tothe display surface of the transflective liquid crystal display device1. The pixel PX has a square shape in the plan view, and theintersection point of diagonal lines thereof is the center PXC of thepixel PX.

The sub-pixels 50B, 50R, 50G, and 50W are partitioned by a space 65 _(A)extending in the column direction (Y-direction) and a space 65 _(B)extending in the row direction (X-direction). The first divided pixels50B1, 50R1, 50G1, and 50W1 and the second divided pixels 50B2, 50R2,50G2, and 50W2 are partitioned by a space 65 _(AI) extending in thecolumn direction (Y-direction) and a space 65 _(BI) extending in the rowdirection (X-direction), respectively.

The space 65 _(AI) and the space 65 _(BI) do not contribute toreflective display with the divided electrodes 501B1, 501R1, 501G1, and501W1 and the divided electrodes 501B2, 501R2, 501G2, and 501W2 asreflective electrodes. Smaller areas of the space 65 _(AI) and the space65 _(BI) lead to an increase in the effective reflection area ratio,that is, an area ratio between the reflective electrode and the space 65_(AI) and the space 65 _(BI) in one pixel PX. As a result, in thereflective liquid crystal display device and the transflective liquidcrystal display device 1, it is possible to minimize influence on thedisplay quality (deterioration in the display quality) in the reflectivedisplay due to the division of the sub-pixels 50B, 50R, 50G, and 50W.

In the case of a transmissive liquid crystal display device, smallerareas of the space 65 _(AI) and the space 65 _(BI) lead to larger areasof the first divided pixels 50B1, 50R1, 50G1, and 50W1 and the seconddivided pixels 50B2, 50R2, 50G2, and 50W2 with respect to the sub-pixels50B, 50R, 50G, and 50W, respectively. As a result, it is possible tosuppress reduction of the display region caused by dividing thesub-pixel 50, so that it is possible to minimize the influence on thedisplay quality (deterioration in the display quality). The same appliesto the transflective liquid crystal display device 1 in a transmissivemode.

In the pixel PX, the first divided pixels 50B1, 50R1, 50G1, and 50W1corresponding to the least significant bit are arranged around thecenter PXC of the pixel PX and closest to the center PXC. In the pixelPX, the second divided pixels 50B2, 50R2, 50G2, and 50W2 as displayregions corresponding to a higher significant bit of the area coveragemodulation are arranged away from the center PXC of the pixel PX. Thepixel PX with such a structure has smaller lengths of the space 65 _(AI)and the space 65 _(BI), so that the effective reflection area ratio canbe enhanced. As a result, the pixel PX has improved display quality inthe reflective display.

The sub-pixels 50B, 50R, 50G, and 50W have a square shape in a planview. The first divided pixels 50B1, 50R1, 50G1, and 50W1 has a squareshape in a plan view. The second divided pixels 50B2, 50R2, 50G2, and50W2 has substantially an L-shape in which one corner of a square isremoved in a plan view.

The first divided pixels 50B1, 50R1, 50G1, and 50W1 include couplingparts CB1, CR1, CG1, and CW1 through which a signal from the signal line61 is applied to the divided electrodes 501B1, 501R1, 501G1, and 501W1,respectively. The second divided pixels 50B2, 50R2, 50G2, and 50W2include coupling parts CB2, CR2, CG2, and CW2 through which the signalfrom the signal line 61 is applied to the divided electrodes 501B2,501R2, 501G2, and 501W2, respectively.

The coupling parts CB1, CR1, CG1, and CW1 of the respective firstdivided pixels 50B1, 50R1, 50G1, and 50W1 corresponding to the leastsignificant bit are arranged close to the center PXC of the pixel PX.The spacer SP illustrated in FIG. 4 is arranged at the coupling partsCB1, CR1, CG1, and CW1 concentrated around the center PXC of the pixelPX. The coupling parts CB1, CR1, CG1, and CW1 are regions where thedivided electrodes 501B1, 501R1, 501G1, and 501W1 as reflectiveelectrodes do not reflect light. By arranging the spacer SP at thecoupling parts CB1, CR1, CG1, and CW1, it is possible to minimizereduction in reflection efficiency of light due to the spacer SP. Alsoin the transmissive liquid crystal display device, it is possible tominimize shielding of the transmitted light due to the spacer SP.

FIG. 11 is a diagram illustrating gradation expression with the pixel ofthe transflective liquid crystal display device according to the presentembodiment. FIG. 11 illustrates a state in which four pixels PXz, PXo,PXt, and PXs express a gradation of zero, a gradation of one, agradation of two, and a gradation of three, respectively, in this order.In a gradation of zero, the brightness of the pixel PX is 0. As thegradation number increases, the brightness of the pixel PX increases.The pixel PXz has a gradation of zero where all of the first dividedpixels 50B1, 50R1, 50G1, and 50W1 and the second divided pixels 50B2,50R2, 50G2, and 50W2 are in the “OFF” state. The pixel PXo has agradation of one where all of the first divided pixels 50B1, 50R1, 50G1,and 50W1 are in the “ON” state, and all of the second divided pixels50B2, 50R2, 50G2, and 50W2 are in the “OFF” state. The pixel PXt has agradation of two where all of the first divided pixels 50B1, 50R1, 50G1,and 50W1 are in the “OFF” state, and all of the second divided pixels50B2, 50R2, 50G2, and 50W2 are in the “ON” state. The pixel PXs has agradation of three where all of the first divided pixels 50B1, 50R1,50G1, and 50W1 and the second divided pixels 50B2, 50R2, 50G2, and 50W2are in the “ON” state. As illustrated in FIG. 11, even when the pixelsPXz, PXo, PXt, and PXs are expressed in gradations different from eachother, each of the gradations can be displayed in a clearlydistinguishable manner. In this way, the transflective liquid crystaldisplay device 1 including the pixels PXz, PXo, PXt, and PXs can reducedegradation in gradation expression. Similarly to the transflectiveliquid crystal display device 1, even the transmissive liquid crystaldisplay device and the transflective liquid crystal display device canreduce degradation in gradation expression if they include the pixelsPXz, PXo, PXt, and PXs.

FIG. 12 is an enlarged view of a coupling part of the first dividedpixel and the second divided pixel. In the following description, thedivided electrodes 501B1, 501R1, 501G1, and 501W1 and the dividedelectrode 501B2, 501R2, 501G2, 501W2 will be described as the reflectiveelectrode 63. The coupling parts CB1, CR1, CG1, and CW1 and the couplingparts CB2, CR2, CG2, and CW2 will be described as a coupling part CP.

The planarization film 15 formed above a surface of the first substrate14 has a double-layer structure in which a first planarization layer 15Aand a second planarization layer 15B are laminated in this order. On asurface of the second planarization layer 15B, formed is the reflectiveelectrode 63 as an electrode corresponding to the first divided pixels50B1, 50R1, 50G1, and 50W1 and the second divided pixels 50B2, 50R2,50G2, and 50W2. The first planarization layer 15A is formed between thesecond planarization layer 15B and a signal supply conductor 67 forsupplying a video signal to each of the pixels PX, more specifically,each of the first divided pixels 50B1, 50R1, 50G1, and 50W1 and thesecond divided pixels 50B2, 50R2, 50G2, and 50W2. A conductor 66 isprovided between the first planarization layer 15A and the secondplanarization layer 15B. The conductor 66 electrically couples thereflective electrode 63 and the signal supply conductor 67. Theconductor 66 and the reflective electrode 63 are coupled at the couplingpart CP. The coupling part CP is a part where the second planarizationlayer 15B is partially removed to the conductor 66 formed on the surfaceof the first planarization layer 15A, and the reflective electrode 63formed on the surface of the second planarization layer 15B and thesignal supply conductor 67 are electrically coupled. A smaller thicknessof the second planarization layer 15B leads to a smaller inside diameterof the coupling part CP.

The conductor 66 is made of ITO, for example. The signal supplyconductor 67 corresponds to the common connection node N_(out) of theother terminals of the switch elements 55 and 56 illustrated in FIG. 8,for example. The first planarization layer 15A is partially removed tothe signal supply conductor 67, and the conductor 66 formed on thesurface of the first planarization layer 15A is electrically coupled tothe signal supply conductor 67.

In this way, in the present embodiment, the planarization film 15 isconfigured to have a double-layer structure, and the reflectiveelectrode 63 and the signal supply conductor 67 are electrically coupledto each other through the conductor 66 provided between the firstplanarization layer 15A and the second planarization layer 15B. Withsuch a structure, the coupling part CP can be provided at an optionalposition. As a result, it is possible to relieve restriction on theposition of the coupling part CP due to the layout of wiring includingthe signal supply conductor 67 formed on the first substrate 14. As aresult, it is possible to relatively easily achieve a structure in whichthe divided pixel corresponding to the least significant bit is arrangedclosest to the center of the pixel and the divided pixel correspondingto a higher bit is arranged at the outside thereof.

FIG. 13 is a diagram illustrating one sub-pixel. In the followingdescription, the sub-pixels 50B, 50R, 50G, and 50W included in the pixelPX illustrated in FIG. 11 will be generalized to be denoted as asub-pixel 50S. The first divided pixels 50B1, 50R1, 50G1, and 50W1 willbe generalized to be denoted as a first divided pixel 50S1. The seconddivided pixels 50B2, 50R2, 50G2, and 50W2 will be generalized to bedenoted as a second divided pixel 50S2. In this example, the sub-pixel50S has a square shape of which side length is 1. The first dividedpixel 50S1 has a rectangular (including a square) shape of which thelength of one side is “a” and the length of the other side is “b”.

In the area coverage modulation, a ratio (area ratio) between the area(a×b) of the first divided pixel 50S1 and the area (1−a×b) of the seconddivided pixel 50S2 needs to have the relation: (a×b):(1−a×b)=1:2.Assuming that K=a+b, the effective reflection area is largest when K issmallest. The area ratio described above gives b=1/(3×a), so thatK=a+1/(3×a). When K is differentiated with respect to “a”, K′=1−3/a², sothat “a” is 1/√3 when K is smallest, that is, K′=0. The relation betweenb=1/(3×a) and a=1/√3 gives b=1/√3. That is, when the second dividedpixel 50S2 has a square shape, it is preferred that the first dividedpixel 50S1 has a square shape in which a=b to maximize the effectivereflection area. In this case, a ratio between the length of the sidesof the second divided pixel 50S2 and the length of the sides of thefirst divided pixel 50S1 is 1:1/√3. It is not excluded that the firstdivided pixel 50S1 has a rectangular shape having the long side and theshort side.

Comparison Between the Present Embodiment and a First ComparativeExample

FIG. 14 is a diagram illustrating gradation expression with the pixelaccording to a first comparative example. In the first comparativeexample, pixels PX1z, PX1o, PX1t, and PX1s has a structure in whichsub-pixels extending in the Y-direction are arranged in the X-direction.When not being distinguished, they are referred to as a pixel PX1. Asub-pixel representing red includes a first divided pixel 150R1 and asecond divided pixel 150R2. A sub-pixel representing green includes afirst divided pixel 150G1 and a second divided pixel 150G2. A sub-pixelrepresenting blue includes a first divided pixel 150B1 and a seconddivided pixel 150B2. A sub-pixel representing white includes a firstdivided pixel 150W1 and a second divided pixel 150W2.

In the first comparative example, the pixel PX1z expresses a gradationof zero, the pixel PX1o expresses a gradation of one, the pixel PX1texpresses a gradation of two, and the pixel PX1s expresses a gradationof three. In this case, the same display as the pixel PX1z displaying ina gradation of zero appears at a portion where the pixel PX1o displayingin a gradation of one is adjacent to the pixel PX1t displaying in agradation of two in the Y-direction. As a result, in the firstcomparative example, it is difficult to clearly distinguish and displayeach of the gradations when the four pixels PX1z, PX1o, PX1t, and PX1sarranged in a square shape display in gradations different from eachother. In contrast, in the present embodiment, as illustrated in FIG.11, each of the gradations can be displayed in a clearly distinguishablemanner even when the four pixels PXz, PXo, PXt, and PXs arranged in asquare shape display in gradations different from each other.

In the first comparative example, each pixel PX1 includes three spaces65 _(A) extending in the Y-direction and one space 65 _(B) extending inthe X-direction. The pixel PX1 has a square shape, and each of thespaces 65 _(A) and the space 65 _(B) is parallel to any one side of thepixel PX1. Assuming that the length thereof is 1, the total length ofthe spaces 65 _(A) and the space 65 _(B) included in one pixel PX1 is 4.

In the present embodiment, as illustrated in FIG. 10, the pixel PXincludes one space 65 _(A) and two spaces 65 _(AI) extending in theY-direction, and one space 65 _(B) and two spaces 65 _(BI) extending inthe X-direction. The pixel PX has a square shape, and each of the space65 _(A), spaces 65 _(AI), space 65 _(B), and spaces 65 _(BI) is parallelto any one side of the pixel PX1. The first divided pixels 50B1, 50R1,50G1, and 50W1 has a square shape, and an area ratio thereof withrespect to the second divided pixels 50B2, 50R2, 50G2, and 50W2 is 1:2.In this case, a ratio between the sides of each sub-pixel 50B, 50R, 50G,and 50W having a square shape included in the pixel PX and the sides ofeach first divided pixels 50B1, 50R1, 50G1, and 50W1 having a squareshape is 1:1/√3. Assuming that the length of the space 65 _(A) and thespace 65 _(B) is 1, the length of the space 65 _(AI) and the space 65_(BI) is √3. Accordingly, the total length of the space 65 _(A), thespaces 65 _(AI), the space 65 _(B), and the spaces 65 _(BI) included inone pixel PX is given by: 2+4/√3=4.31.

Assuming that the widths of the space 65 _(A), the space 65 _(AI), thespace 65 _(B), and the space 65 _(BI) are the same in the firstcomparative example and the present embodiment, the total length of thespace 65 _(A), the space 65 _(AI), the space 65 _(B), and the space 65_(BI) included in the pixel PX of the present embodiment is slightlylarger than the total length of the space 65 _(A) and the space 65 _(B)included in the pixel PX1 of the first comparative example. As a result,in the present embodiment, an effective reflection area ratiosubstantially equivalent to that in the first comparative example can besecured, so that the display quality in the reflective display issubstantially equivalent to that of the first comparative example.

Comparison Between the Present Embodiment and a Second ComparativeExample

FIG. 15 is a diagram illustrating gradation expression with a pixelaccording to a second comparative example. In the second comparativeexample, pixels PX2z, PX2o, PX2t, and PX2s has a structure in whichsub-pixels extending in the Y-direction are arranged in the Y-direction.When not being distinguished, they are referred to as a pixel PX2. Asub-pixel representing red includes a first divided pixel 250R1 and twosecond divided pixels 250R2 arranged at both sides in the Y-direction ofthe first divided pixel 250R1. A sub-pixel representing green includes afirst divided pixel 250G1 and two second divided pixels 250G2 arrangedat both sides in the Y-direction of the first divided pixel 250G1. Asub-pixel representing blue includes a first divided pixel 250B1 and twosecond divided pixels 250B2 arranged at both sides in the Y-direction ofthe first divided pixel 250B1. A sub-pixel representing white includes afirst divided pixel 250W1 and two second divided pixels 250W2 arrangedat both sides in the Y-direction of the first divided pixel 250W1.

In the second comparative example, the pixel PX2z expresses a gradationof zero, the pixel PX2o expresses a gradation of one, the pixel PX2texpresses a gradation of two, and the pixel PX2s expresses a gradationof three. In this case, as illustrated in FIG. 15, each of thegradations can be displayed in a clearly distinguishable manner evenwhen the four pixels PX2z, PX2o, PX2t, and PX2s arranged in a squareshape display in gradations different from each other. The same appliesto four pixels PXz, PXo, PXt, and PXs of the present embodimentillustrated in FIG. 11.

In the second comparative example, each pixel PX2 includes three spaces65 _(A) extending in the Y-direction and two spaces 65 _(B) extending inthe X-direction. The pixel PX2 has a square shape, and each of thespaces 65 _(A) and the spaces 65 _(B) is parallel to any one side of thepixel PX2. Assuming that the length thereof is 1, the total length ofthe spaces 65 _(A) and the spaces 65 _(B) included in one pixel PX2 is5. As described above, in the present embodiment, the total length ofthe space 65 _(A), the spaces 65 _(AI), the space 65 _(B), and thespaces 65 _(BI) included in one pixel PX is given by: 2+4/√3=4.31.

Assuming that the widths of the space 65 _(A), the space 65 _(AI), thespace 65 _(B), and the space 65 _(BI) are the same in the secondcomparative example and the present embodiment, the total length of thespace 65 _(A), the space 65 _(AI), the space 65 _(B), and the space 65_(BI) included in the pixel PX of the present embodiment is smaller thanthe total length of the space 65 _(A) and the space 65 _(B) included inthe pixel PX2 of the second comparative example. Accordingly, theeffective reflection area ratio in the present embodiment is larger thanthat in the second comparative example, so that the display quality inthe reflective display is higher than that in the second comparativeexample.

Comparison Between the Present Embodiment and a Third ComparativeExample

FIG. 16 is a diagram illustrating a pixel according to a thirdcomparative example. FIG. 17 is a diagram illustrating gradationexpression with the pixel according to the third comparative example. Inthe third comparative example, the pixel PX3 has a structure in whichsub-pixels extending in the X-direction are arranged in the Y-direction.A sub-pixel representing blue includes a first divided pixel 350B1extending in the X-direction and two second divided pixels 350B2 thatare arranged at both sides in the Y-direction of the first divided pixel350B1 and extend in the X-direction. A sub-pixel representing redincludes a first divided pixel 350R1 extending in the X-direction andtwo second divided pixels 350R2 that are arranged at both sides in theY-direction of the first divided pixel 350R1 and extend in theX-direction. A sub-pixel representing green includes a first dividedpixel 350G1 extending in the X-direction and two second divided pixels350G2 that are arranged at both sides in the Y-direction of the firstdivided pixel 350G1 and extend in the X-direction. A sub-pixelrepresenting white includes a first divided pixel 350W1 extending in theX-direction and two second divided pixels 350W2 that are arranged atboth sides in the Y-direction of the first divided pixel 350W1 andextend in the X-direction.

In the third comparative example, a pixel PX3z illustrated in FIG. 17expresses a gradation of zero, a pixel PX3o expresses a gradation ofone, a pixel PX3t expresses a gradation of two, and a pixel PX3sexpresses a gradation of three. In this case, as illustrated in FIG. 17,each of the gradations can be displayed in a clearly distinguishablemanner even when the four pixels PX3z, PX3o, PX3t, and PX3s arranged ina square shape display in gradations different from each other. The sameapplies to four pixels PXz, PXo, PXt, and PXs of the present embodimentillustrated in FIG. 11.

In the third comparative example, as illustrated in FIG. 16, each pixelPX3 includes one space 65 _(A) extending in the Y-direction and fivespaces 65 _(B) extending in the X-direction. The pixel PX3 has a squareshape, and each of the space 65 _(A) and the spaces 65 _(B) is parallelto any one side of the pixel PX3. Assuming that the length thereof is 1,the total length of the space 65 _(A) and the spaces 65 _(B) included inone pixel PX3 is 7. As described above, in the present embodiment, thetotal length of the space 65 _(A), the spaces 65 the space 65 _(B), andthe spaces 65 _(BI) included in one pixel PX is given by: 2+4/√3=4.31.

Assuming that the widths of the space 65 _(A), the space 65 _(AI), thespace 65 _(B), and the space 65 _(BI) are the same in the thirdcomparative example and the present embodiment, the total length of thespace 65 _(A), the space 65 _(AI), the space 65 _(B), and the space 65_(BI) included in the pixel PX of the present embodiment is smaller thanthe total length of the space 65 _(A) and the space 65 _(B) included inthe pixel PX3 of the third comparative example. Specifically, the totallength of the spaces in the present embodiment is substantially 60% ofthat in the third comparative example. Accordingly, the effectivereflection area ratio in the present embodiment is larger than that inthe third comparative example, so that the display quality in thereflective display is higher than that in the third comparative example.

As described above, according to the present embodiment, one pixel has astructure in which each divided pixel corresponding to the leastsignificant bit is arranged closest to the center of the pixel, and thedivided pixel corresponding to a higher significant bit of the areacoverage modulation is arranged away from the center of the pixel andaround the center of the pixel. Accordingly, the present embodiment canachieve clear gradation expression and suppress reduction in theeffective reflection area ratio or in the area of the divided pixelsthat contributes to display. As a result, in the present embodiment, itis possible to reduce effects on display quality caused by dividing thesub-pixel, and also reduce degradation in gradation expression.

1-7. First Modification

FIG. 18 is a diagram illustrating a pixel according to a firstmodification of the present embodiment. Although the pixel PX describedabove is represented in 2 bits, a pixel PXa is represented in 3 bits.The pixel PXa can express 8-step gradation. The pixel PXa includes asub-pixel 50Ba representing blue, a sub-pixel 50Ra representing red, asub-pixel 50Ga representing green, and a sub-pixel 50Wa representingwhite. The sub-pixel 50Ba includes a first divided pixel 50B1, a seconddivided pixel 50B2, and a third divided pixel 50B3. The sub-pixel 50Raincludes a first divided pixel 50R1, a second divided pixel 50R2, and athird divided pixel 50R3. The sub-pixel 50Ga includes a first dividedpixel 50G1, a second divided pixel 50G2, and a third divided pixel 50G3.The sub-pixel 50Wa includes a first divided pixel 50W1, a second dividedpixel 50W2, and a third divided pixel 50W3.

The first divided pixels 50B1, 50R1, 50G1, and 50W1 are display regionsof the sub-pixels 50Ba, 50Ra, 50Ga, and 50Wa corresponding to the leastsignificant bit, respectively. The second divided pixels 50B2, 50R2,50G2, and 50W2 are display regions of the sub-pixels 50Ba, 50Ra, 50Ga,and 50Wa corresponding to the next less significant bit than the leastsignificant bit, respectively. The second divided pixels 50B3, 50R3,50G3, and 50W3 are display regions of the sub-pixels 50Ba, 50Ra, 50Ga,and 50Wa corresponding to the second higher bit than the leastsignificant bit, respectively. In the present modification, the thirddivided pixels 50B3, 50R3, 50G3, and 50W3 correspond to the mostsignificant bits of the respective sub-pixels 50Ba, 50Ra, 50Ga, and50Wa.

The first divided pixels 50B1, 50R1, 50G1, and 50W1 are arranged aroundthe center PXCa of the pixel PXa. They are arranged closest to thecenter PXCa. The second divided pixels 50B2, 50R2, 50G2, and 50W2corresponding to a higher bit than the first divided pixels 50B1, 50R1,50G1, and 50W1 are arranged at the outside of the first divided pixels50B1, 50R1, 50G1, and 50W1. They are arranged to surround the centerPXCa of the pixel PXa. The third divided pixels 50B3, 50R3, 50G3, and50W3 corresponding to a higher bit than the second divided pixels 50B2,50R2, 50G2, and 50W2 are arranged at the outside of the second dividedpixels 50B2, 50R2, 50G2, and 50W2. They are also arranged to surroundthe center PXCa of the pixel PXa.

The first divided pixels 50B1, 50R1, 50G1, and 50W1 include the couplingparts CB1, CR1, CG1, and CW1, respectively, at which each dividedelectrode thereof is electrically coupled to the conductor 66illustrated in FIG. 12. The second divided pixels 50B2, 50R2, 50G2, and50W2 include the coupling parts CB2, CR2, CG2, and CW2, respectively, atwhich each divided electrode thereof is electrically coupled to theconductor 66 illustrated in FIG. 12. The third divided pixels 50B3,50R3, 50G3, and 50W3 include coupling parts CB3, CR3, CG3, and CW3,respectively, at which each divided electrode thereof is electricallycoupled to the conductor 66 illustrated in FIG. 12.

With such a structure, the pixel PXa can express 8-step gradation.Similarly to the present embodiment described above, the pixel PXa canachieve clear gradation expression and enhance the effective reflectionarea ratio to improve the display quality in the reflective display.

1-8. Second Modification

FIG. 19 is a diagram illustrating a pixel according to a secondmodification of the present embodiment. The pixel PX and the pixel PXadescribed above represent the four colors of blue, red, green, andwhite, whereas a pixel PXb represents three colors of blue, red, andgreen. The pixel PXb is represented in 2 bits and can express 4-stepgradation. The pixel PXb has a hexagonal shape (in this example, aregular hexagonal shape) in a plan view. Specifically, the pixel PXb isthe inside region surrounded by a space 65 _(C) dividing the pixel PXbfrom adjacent pixels PXb. The pixel PXb includes a sub-pixel 50Bbrepresenting blue, a sub-pixel 50Rb representing red, and a sub-pixel50Gb representing green.

The three sub-pixels 50Bb, 50Rb, and 50Gb are display regions in a rangeof central angles θb, θr, and θg, respectively, with respect to thecenter PXCb of the pixel PXb. The sub-pixels 50Bb, 50Rb, and 50Gb areinside regions surrounded by two spaces 65 _(D) radially extending fromthe center PXCb of the pixel PXb and the space 65 _(C). The sub-pixels50Bb, 50Rb, and 50Gb has a diamond shape. The areas of the respectivesub-pixels 50Bb, 50Rb, and 50Gb are the same. Accordingly, the centralangles are: θb=θr=θg=120°. The areas of the sub-pixels 50Bb, 50Rb, and50Gb may be changed depending on the characteristics and the like of thecolor filter 22 corresponding to the sub-pixels 50Bb, 50Rb, and 50Gb.These areas can be changed by making the central angles θb, θr, and θgdifferent from each other.

The sub-pixel 50Bb includes a first divided pixel 50B1 and a seconddivided pixel 50B2. The sub-pixel 50Rb includes a first divided pixel50R1 and a second divided pixel 50R2. The sub-pixel 50Gb includes afirst divided pixel 50G1 and a second divided pixel 50G2. The firstdivided pixels 50B1, 50R1, and 50G1 are display regions of thesub-pixels 50Bb, 50Rb, and 50Gb corresponding to the least significantbit. The second divided pixels 50B2, 50R2, and 50G2 are display regionsof the sub-pixels 50Bb, 50Rb, and 50Gb corresponding to the mostsignificant bits of the respective sub-pixels 50Bb, 50Rb, and 50Gb.

The first divided pixels 50B1, 50R1, and 50G1 are regions surrounded bythe space 6S partitioning the sub-pixels 50Bb, 50Rb, and 50Gb into tworegions and the two spaces 65 _(D) radially extending from the centerPXCb of the pixel PXb. The second divided pixels 50B2, 50R2, and 50G2are regions surrounded by the space 65 _(CI) partitioning each of thesub-pixels 50Bb, 50Rb, and 50Gb into two regions, the two spaces 65 _(D)radially extending from the center PXbC of the pixel PXb, and the space65 _(C).

The first divided pixels 50B1, 50R1, and 50G1 are arranged around thecenter PXCb of the pixel PXb. They are arranged closest to the centerPXCb. The second divided pixels 50B2, 50R2, and 50G2 corresponding to ahigher bit (in the present modification, the most significant bit) thanthe first divided pixels 50B1, 50R1, and 50G1 are arranged at theoutside of the first divided pixels 50B1, 50R1, and 50G1. They arearranged to surround the center PXCb of the pixel PXb.

The first divided pixels 50B1, 50R1, and 50G1 include the coupling partsCB1, CR1, and CG1, respectively, at which each divided electrode thereofis electrically coupled to the conductor 66 illustrated in FIG. 12. Thesecond divided pixels 50B2, 50R2, and 50G2 include the coupling partsCB2, CR2, and CG2, respectively, at which each divided electrode thereofis electrically coupled to the conductor 66 illustrated in FIG. 12.

With such a structure, the pixel PXb can express 4-step gradation withthree-color display of blue, red, and green. Similarly to the presentembodiment described above and the modifications thereof, the pixel PXbcan achieve clear gradation expression and enhance the effectivereflection area ratio to improve the display quality in the reflectivedisplay. Although the present embodiment, the first modification, andthe second modification describe an example of having three or foursub-pixels, the number of sub-pixels is not limited thereto. Forexample, one pixel may have five or more sub-pixels.

2. Electronic Apparatus

The transflective liquid crystal display device 1 according to thepresent disclosure described above can be used as a display unit(display device) of an electronic apparatus in various fields thatdisplays a video signal input to the electronic apparatus or a videosignal generated in the electronic apparatus as an image or video. Thefollowing describes a specific example of the electronic apparatus towhich the transflective liquid crystal display device 1 is applied as adisplay unit, that is, the electronic apparatus according to the presentdisclosure.

Application Example 1

The electronic apparatus illustrated in FIG. 20 is a televisionapparatus to which the transflective liquid crystal display device 1 isapplied. For example, the television apparatus includes a video displayscreen unit 510 including a front panel 511 and a filter glass 512, andthe transflective liquid crystal display device 1 is applied to thevideo display screen unit 510. That is, the screen of the televisionapparatus may have a function for detecting a touch operation inaddition to a function for displaying an image.

Application Example 2

The electronic apparatus illustrated in FIG. 21 and FIG. 22 is a digitalcamera to which the transflective liquid crystal display device 1 isapplied. For example, the digital camera includes a flash light emittingunit 521, a display unit 522, a menu switch 523, and a shutter button524, and the transflective liquid crystal display device 1 is applied tothe display unit 522. Accordingly, the display unit 522 of the digitalcamera may have a function for detecting a touch operation in additionto a function for displaying an image.

Application Example 3

The electronic apparatus illustrated in FIG. 23 represents the externalappearance of a video camera to which the transflective liquid crystaldisplay device 1 is applied. For example, the video camera includes amain body part 531, a lens 532 for photographing a subject provided onthe front side surface of the main body part 531, a start/stop switch533 for photographing, and a display unit 534. The transflective liquidcrystal display device 1 is applied to the display unit 534.Accordingly, the display unit 534 of the video camera may have afunction for detecting a touch operation in addition to a function fordisplaying an image.

Application Example 4

The electronic apparatus illustrated in FIG. 24 is a laptop personalcomputer to which the transflective liquid crystal display device 1 isapplied. For example, the laptop personal computer includes a main body541, a keyboard 542 for input operation of characters and the like, anda display unit 543 for displaying an image. The transflective liquidcrystal display device 1 is applied to the display unit 543.Accordingly, the display unit 543 of the laptop personal computer mayhave a function for detecting a touch operation in addition to afunction for displaying an image.

Application Example 5

The electronic apparatus illustrated in FIG. 25 to FIG. 31 is a mobilephone to which the transflective liquid crystal display device 1 isapplied. FIG. 25 is a front view of the mobile phone in an open state,FIG. 26 is a right side view of the mobile phone in the open state, FIG.27 is a top view of the mobile phone in a folded state, FIG. 28 is aleft side view of the mobile phone in the folded state, FIG. 29 is aright side view of the mobile phone in the folded state, FIG. 30 is arear view of the mobile phone in the folded state, and FIG. 31 is afront view of the mobile phone in the folded state. For example, themobile phone is formed by connecting an upper housing 551 and a lowerhousing 552 with a connecting part (hinge part) 553, and includes adisplay device 554, a sub-display device 555, a picture light 556, and acamera 557. The transflective liquid crystal display device 1 isattached as the display device 554. Accordingly, the display device 554of the mobile phone may have a function for detecting a touch operationin addition to a function for displaying an image.

Application Example 6

The electronic apparatus illustrated in FIG. 32 is an informationportable terminal that operates as a portable computer, amultifunctional mobile phone, a portable computer allowing voicecommunication, or a communicable portable computer, and may be called asmart phone and/or a tablet terminal. For example, the informationportable terminal includes a display unit 602 arranged on a surface of ahousing 601. The display unit 562 is the transflective liquid crystaldisplay device 1.

5. Aspects of Present Disclosure

The present disclosure includes aspects as follows.

(1) A display device comprising:

a plurality of pixels each including a plurality of sub-pixels, wherein

each of the sub-pixels is arranged around center of the correspondingpixel and divided into a plurality of display regions to perform N-bitarea coverage modulation by a combination of the display regions, and

the display regions are arranged in such a manner that:

-   -   a display region corresponding to a least significant bit of the        area coverage modulation is arranged closest to the center of        the corresponding pixel; and    -   a display region corresponding to a higher significant bit of        the area coverage modulation is arranged around the center of        the pixel and further from the center of the corresponding pixel        (N is a natural number of 2 or more).

(2) The display device according to (1), further comprising:

a second planarization layer on which a plurality of electrodescorresponding to the respective display regions are formed;

a first planarization layer formed between the second planarizationlayer and a first conductor for applying a video signal to be given tothe corresponding electrode; and

a second conductor arranged between the first planarization layer andthe second planarization layer to electrically couple the firstconductor to the corresponding electrode.

(3) The display device according to (2), further comprising:

a liquid crystal layer arranged between the electrodes and a counterelectrode opposite to the electrodes, wherein

each of the pixels is provided at a position close to the center thereofwith a coupling part at which the electrode corresponding to the displayregion corresponding to the least significant bit is coupled to thecorresponding second conductor, and arranges a spacer for forming aspace to form the liquid crystal layer at the coupling part.

(4) The display device according to (1), wherein the sub-pixels and thedisplay regions corresponding to the least significant bit have a squareshape.

(5) The display device according to (2), wherein the electrodes reflectincident light.

(6) An electronic apparatus comprising the display device according to(1).

The present disclosure provides a display device and an electronicapparatus including the same. The display device includes a plurality ofpixels each including a plurality of sub-pixels, the sub-pixels arearranged around the center of the pixel and divided into a plurality ofdisplay regions, and N-bit area coverage modulation can be performed bya combination of the display regions. The display region correspondingto the least significant bit is arranged closest to the center of thepixel. The display region corresponding to a higher significant bit ofthe area coverage modulation is arranged around the center of the pixeland away from the center of the pixel. N is a natural number of 2 ormore.

The pixel according to the present disclosure has a structure in whichthe display region corresponding to the least significant bit isarranged closest to the center of the pixel, and the display regioncorresponding to a higher significant bit of the area coveragemodulation is arranged away from the center of the pixel. That is, thedisplay region corresponding to a higher significant bit of the areacoverage modulation is arranged around the center of the pixel andaround the display region corresponding to a lower bit. Accordingly, thedisplay device and the electronic apparatus including the same accordingto the present disclosure can achieve clear gradation expression andsuppress reduction in an effective reflection area ratio or in the areaof divided pixels that contributes to display. As a result, in thepresent embodiment, it is possible to reduce effects on display qualitycaused by dividing the sub-pixel, and also reduce degradation ingradation expression.

According to the present disclosure, when the area coverage modulationis performed, it is possible to reduce effects on the display qualitycaused by dividing the pixel, and reduce degradation in gradationexpression.

What is claimed is:
 1. A display device comprising: a plurality ofpixels each including a plurality of sub-pixels, each of which isarranged around center of the corresponding pixel, wherein each of thepixels is divided by first lines of gaps that radially extend from thecenter of the corresponding pixel toward outer edges of thecorresponding pixel, into a plurality of display regions including afirst display region and the second display region to perform N-bit areacoverage modulation (N is a natural number of 2 or more) by acombination of the display regions, and wherein the display regions arearranged in such a manner that: the first display region correspondingto a least significant bit of the area coverage modulation is arrangedclosest to the center of the corresponding pixel, the first displayregion having first coupling parts at a position close to the center ofthe corresponding pixel; and the second display region corresponding toa most significant bit of the area coverage modulation is arrangedaround the center of the pixel and further from the center of thecorresponding pixel, the second display region having second couplingparts at a position at a corner of the corresponding pixel.
 2. Thedisplay device according to claim 1, further comprising: a secondplanarization layer on which a plurality of electrodes corresponding tothe respective display regions are formed; a first planarization layerformed between the second planarization layer and a first conductor forapplying a video signal to be given to the corresponding electrode; anda second conductor arranged between the first planarization layer andthe second planarization layer to electrically couple the firstconductor to the corresponding electrode.
 3. The display deviceaccording to claim 2, further comprising: a liquid crystal layerarranged between the electrodes and a counter electrode opposite to theelectrodes, wherein each of the first and second coupling parts iscoupled to the corresponding second conductor, and spacers for forming aspace to form the liquid crystal layer are formed at the first couplingparts.
 4. The display device according to claim 2, wherein theelectrodes reflect incident light.
 5. The display device according toclaim 1, wherein the sub-pixels and the display regions corresponding tothe least significant bit have a square shape.
 6. An electronicapparatus comprising the display device according to claim
 1. 7. Thedisplay device according to claim 1, wherein each of the pixels isdivided by the first lines into four equal areas corresponding to thesub-pixels, and the sub-pixels are a first sub-pixel, a secondsub-pixel, a third sub-pixel, and a fourth sub-pixel.
 8. The displaydevice according to claim 7, wherein each of the sub-pixels are dividedinto the first display region, the second display region, and a thirddisplay region that corresponds to a higher significant bit of the areacoverage modulation than the first display region and less significantbit of the area coverage modulation than the second display region. 9.The display device according to claim 8, wherein the third displayregion is arranged around the first display region, the third displayregion has third coupling parts each arranged at a position that is acorner of the respective sub-pixel corresponding to a corner of thethird display region.
 10. The display device according to claim 1,wherein each of the pixels has a hexagonal shape, each of the pixels isdivided by the first lines into three equal areas corresponding to thesub-pixels, and the sub-pixels are a first sub-pixel, a secondsub-pixel, and a third sub-pixel.